Trypanosomes and related protozoan parasites cause a range of diseases man and his livestock (e.g. Chagas disease and sleeping sickness). The blood-dwelling parasite Trypanosoma brucei escapes immune-destruction through antigenic variation, by periodically changing the production of one variant cell surface glycoprotein (VSG) coat to the next. We will study the genetic basis of immune- evasion. The focus will be on transcriptional control of VSG genes and on understanding the importance of expression site, chromosome and nuclear structure for VSG gene activation. We will also study the biological role of expression site associated genes, that are coordinately transcribed with the VSG gene. We are particularly interested in transcription of VSG genes by a novel type of RNA polymerase that is insensitive to the drug alpha- amanitin. We will characterize this RNA polymerase and compare its transcriptional specificity to that of other eukaryotic RNA polymerases. We will test drugs for their capability to interfere with transcription switching of VSG genes. We will survey the importance of transcription of protein-coding genes by alpha- amanitin insensitive RNA polymerases in trypanosomes and related kinetoplastida. These studies are aimed at understanding the biological role of transcription of protein coding get by RNA polymerase II and another as yet unidentified RNA polymerase. A rationale for drug therapy may result. To facilitate the molecular analysis of these protozoan parasites will further develop a DNA transfection system for T.brucei. We will construct vectors that can be used to introduce foreign genes into trypanosomes. The vectors will be engineered to resemble VSG gene expression sites with which chromosomal rearrangements and transcript control of VSG genes will be studied.